Cellular communication systems are becoming increasingly more important. In such cellular communication systems, a user equipment (UE), such as a mobile phone or cellular computer modems, connects wirelessly to the network via base stations (BSs), that in turn are connected to a backhaul network for forwarding the communication from the user equipment.
An example of such a cellular communication system is the 3GPP (3rd Generation Partnership Project) Long Term Evolution (LTE) system, in the following referred to simply as “LTE”. In LTE, multiple access is achieved using OFDMA (Orthogonal Frequency Division Multiple Access), in which different resource blocks (RBs) can be reserved for different UEs. An RB is built up by a number of sub carriers of an OFDM (Orthogonal Frequency Division Multiplexing) signal during a certain time interval. Duplex communication between a UE and a base station can be accomplished using frequency division duplex (FDD), wherein signals are sent from the UE to the BS in an up-link (UL) frequency band and signals are sent from the BS to the UE in a down-link (DL) frequency band (separate and disjoint from the UL frequency band). Alternatively, time division duplex (TDD) communication between a UE and a base station can be accomplished, wherein signals are sent from the UE to the BS in UL time slots and from the BS to the UE in DL time slots (separate and disjoint from the UL time slots).
In order to better utilize the resources of a cellular communication system, it has been suggested that UEs may engage in so called device-to-device (D2D) communication, wherein the UEs communicate data directly between them, i.e. without sending the data via the cellular communication network node. Such D2D communication may be possible when two UEs are in the proximity of each other. Some aspects of D2D communication are briefly discussed in G. Fodor et al, “Design aspects of network assisted device-to-device communications”, IEEE Communications Magazine, pp 170-177, March 2012.
It is desirable to provide D2D communication capability for a cellular communication network at a relatively low overhead.